1. Field of the Invention
This invention relates to an apparatus and method for determining the measurement accuracy of an uncalibrated field meter, such as a gas meter, by comparing its flow measurement to a master meter of known accuracy.
2. Description of the Related Art
It is known to determine the measurement accuracy of an uncalibrated field meter by comparing its flow measurement to a master meter of known accuracy such as the Model 4 Transfer Prover manufactured by Dresser Measurement, Inc. This is called "transfer proving" and is accomplished by passing a common gas stream through both meters for some known period of time and noting the gas volume registered by each meter. A meter correction factor for the field meter is then determined by mathematically dividing the flow registered by the field meter by the master meter registered flow. Once the correction factor is determined the readings of the field meter can be divided by the correction factor to remove any measurement error in the field meter.
When the gas stream is passed through both the field meter and master meter work is done on the gas. This work causes minor changes in temperature and pressure of the fluid as it enters and exits each meter. Therefore, these changes need to be measured and used to correct the actual gas volume passing through each meter. The accuracy of the field meter can then be defined by the equation: EQU Field Meter Accuracy=V.sub.f /V.sub.m .multidot.P.sub.1 /P.sub.2 .multidot.T.sub.2 /T.sub.1 .multidot.100%,
Where V.sub.f =Field Meter Volume V.sub.m =Master Meter Volume, P.sub.2 =Inlet Pressure of the Master Meter, P.sub.1 =Inlet Pressure of the Field Meter, T.sub.1 =Inlet Gas Temperature of the Field Meter and T.sub.2 =Inlet Gas Temperature of the Master Meter.
Equipment for determining the field meter accuracy can be transported on a cart to the field where the field meter is in use. It is also known, to connect a blower, a master meter and a field meter in such a manner that the blower passes a common fluid or gas stream through both the field meter and master meter. Pressure, temperature, and volume measurement devices are connected to a controller that records all the necessary data during the test and calculates the field meter accuracy. Heretofore, this test has required an operator to step through the test procedure and prompt the controller at each step. This means that a great deal of care and attention by the operator is needed to ensure reliable test results.
U.S. Pat. No. 4,965,756 to Pearman et al. discloses a method and apparatus for calibration of electronic gas meters. Pearman et al. disclose calibrating electronic gas meters using what is commonly referred to as a bell prover. In the bell prover system a bell of known volume is used to pass a known volume of fluid through the meter under test. The volume registered by the meter under test is then compared with the known volume passed through said meter to determine the accuracy of the meter under test. The major disadvantage of bell provers is that they are not suited for portable operations. They must be maintained at substantially constant temperature to deliver accurate results.